1. Field of the Invention
The present invention is directed to an implantable fluid valve for the adjustable limitation of the fluid pressure in the brain of a patient.
2. Description of the Prior Art
Valves that allow a setting of the maximum pressure from the outside of a patient, and automatically allow fluid to flow off given excess pressure, are required for patients whose discharge of fluid from the brain is abnormal.
Valves that can be set from the outside by means of magnetic forces are commercially available. These valves are not MR-compatible. (As used herein, MR stands for magnetic resonance.) Examination of the patient in conventional MR scanners thus is not possible without risk, particularly given flux densities of 1 T and above. A maladjustment of the programmed pressure level or even damage to the implanted valves is a frequent complication even given the use of low-field MR scanners.
Although having parts composed of rubber, a setting of the fluid pressure is not possible at all with a fluid valve disclosed by U.S. Pat. No. 3,595,240, which derives from a time when magnetic resonance systems were not yet known, so that the problem of an MR-compatible fluid valve did not arise at all.
In one embodiment of a cerebrospinal fluid shunt valve disclosed in U.S. Pat. No. 4,551,128, adjustment is possible by only puncturing the scalp to allow access of a screwdriver or the like to an adjustment screw. This is unacceptable in practice particularly because of the risk of infection and moreover this fluid valve has metallic parts that are fundamentally incompatible with MR. In another embodiment of this known valve, magnetic adjustment for the adjustable limitation of the fluid pressure is even worse as to MR compatibility. That embodiment includes magnetic component parts that could create life-threatening complications in conjunction with the extremely high field strengths of the basic magnetic field of an MR system. Thus, this known fluid valve is neither suitable for utilization with MR monitoring observation nor was this even envisioned.
The same is also true of a fluid valve according to U.S. Pat. No. 5,167,615 that likewise contains magnets for setting the respective pressure.
British patent application GB 2 143 008 as well as European patent application 0 233 325 also disclose valves that are not MR-compatible. The use of stainless steel is expressly prescribed in the former which makes this valve non-MR-compatible because MR compatibility not only involves avoiding magnetic components but also avoiding components having good electrical conductivity since considerable artifacts could otherwise arise.